Method for preparing coal to be injected into blast furnace, coal to be injected into blast furnace, and usage of same

ABSTRACT

A method for preparing coal which is to be injected into a blast furnace includes: a step (S 1 ) for analyzing the ash of coal in a raw-coal stage and determining the contents (wt %) of At Si, Ca and Mg in the ash; a step (S 2 ) for deriving the ash melting point of the coal on the basis of the obtained data: a step (S 3 ) for selecting a metal species to be supported on the coal and deriving the amount thereof to be supported on the basis of the obtained data so as to adjust the melting point of the ash of the coal to 1200 to 1400° C.; a step (S 4 ) for making the metal supported on the coal in the derived amount by an ion-exchange method; and a step (S 5 ) for carbonizing the coal obtained in the step ( 4 ).

TECHNICAL FIELD

The present invention relates to a method for preparing blast furnace injection coal, blast furnace injection coal, and a method for using the blast furnace injection coal.

BACKGROUND ART

Blast furnace installations have been configured to be capable of producing pig iron from iron ore by charging starting materials such as iron ore, limestone, and coke through the top of the blast furnace main body into the interior, and injecting hot air and blast furnace injection coal (pulverized coal) as an auxiliary fuel through a tuyere on a lower side of a side portion of the blast furnace main body.

To stably operate the above-described blast furnace installation, the blast furnace injection coal is required to be such that the accretion of ash of the blast furnace injection coal or the occlusion by ash of the blast furnace injection coal should be suppressed in a pathway leading to the tuyere of the blast furnace main body.

For example, it has been proposed to improve the combustibility of blast furnace injection coal by measuring the softening points of ash in pulverized coals in advance, adding a CaO-based flux such as limestone or serpentinite or another pulverized coal to each of the pulverized coals having softening points of ash of lower than 1300° C. in a necessary amount determined based on the softening point of the pulverized coal to adjust the softening point of the ash in the pulverized coal to 1300° C. or higher, and, subsequently, injecting only the pulverized coals whose softening points of ash are 1300° C. or higher into the interior through a tuyere of a blast furnace main body (for example, see Patent Document 1 below).

Furthermore, a blast furnace operation method has been proposed, wherein, for example, any one or two or more of CaO-based, MgO-based, and SiO₂-based fluxes are injected into the interior of a blast furnace through a tuyere (for example, see Patent Document 2 below).

PRIOR ART DOCUMENT Patent Document

Patent Document 1: Japanese Unexamined Patent Application Publication No. H5-156330A

Patent Document 2: Japanese Unexamined Patent Application Publication No. H3-291313A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, in the technique described in Patent Document 1, calcium oxide added as the flux has large particle diameters (fine calcium oxide particles have diameters of about 10 μm), and it takes a long time to uniformly mix the calcium oxide with the slag in the blast furnace. Hence, there is a possibility that the effect of the addition of the flux to elevate the softening point of the blast furnace injection coal tends to be difficult to obtain, also when a large amount of blast furnace injection coal is injected.

In Patent Document 2, described is only a blast furnace operation method which assures fluidity of bosh slag produced in the blast furnace by setting the viscosity at 1450° C. to 10 poise or lower. Therefore, there is a possibility that the accretion of ash of the blast furnace injection coal or the occlusion by ash of the blast furnace injection coal in a pathway leading to the tuyere of the blast furnace main body cannot be suppressed.

From such facts, the present invention has been made to solve the problems described above, and an object of the present invention is to provide a method for preparing blast furnace injection coal which makes it possible to obtain blast furnace injection coal which is resistant to fluidity failure of slag in the blast furnace main body, even when the amount of the coal injected into the blast furnace main body is increased, as well as blast furnace injection coal and a method for using the blast furnace injection coal.

Means for Solving the Problems

A method for preparing blast, furnace injection coal pertaining to a first aspect of the invention which solves the above problems comprises: a first step of analyzing ash of run-of-mine coal and weight percentages of Al, Si, Ca, and Mg in the ash; a second step of deriving an ash melting point of the coal based on data obtained by the analysis; a third step of selecting a metal species to be supported on. the coal and deriving the amount of the metal species to be supported based on data obtained in the first step and the second step to adjust the melting point of the ash of the coal to 1200 to 1400° C.; a fourth step of supporting the metal in the amount to be supported onto the coal by an ion exchange method; and a fifth step of pyrolyzing the coal obtained in the fourth step.

A method for preparing blast furnace injection coal pertaining to a second aspect of the invention which solves the above problems is the method for preparing blast furnace injection coal pertaining to the above-described first aspect of the invention, wherein the metal is at least one of calcium and magnesium.

A method for preparing blast furnace injection coal pertaining to a third aspect of the invention which solves the above problems is the method for preparing blast furnace injection coal pertaining to the above-described first or second aspect of the invention, wherein the coal is thermally treated at 350 to 550° C. in the fifth step to adjust a residual volatile content to 15 to 35%.

A method for preparing blast furnace injection coal pertaining to a fourth aspect of the invention which solves the above problems is the method for preparing blast furnace injection coal pertaining to any one of the above-described first to third aspects of the invention, wherein the amount of the metal to be supported on the coal is 0.2 to 1.55 in terms of (CaO+MgO)/SiO₂ weight ratio.

A method for preparing blast furnace injection coal pertaining to a fifth aspect of the invention which solves the above problems is the method for preparing blast furnace injection coal pertaining to the above-described fourth aspect of the invention, wherein the amount of the metal to be supported on the coal is 0.25 to 1.4 in terms of (CaO+MgO)/SiO₂ weight ratio.

A method for preparing blast furnace injection coal pertaining to a sixth aspect of the invention which solves the above problems is the method for preparing blast furnace injection coal pertaining to the above-described fifth aspect of the invention, wherein the amount of the metal to be supported on the coal is 0.35 to 1 in terms of (CaO+MgO)/SiO₂ weight ratio.

Blast furnace injection coal pertaining to a seventh aspect of the invention which solves the above problems is obtained by the method for preparing blast furnace injection coal pertaining to any one of the above-described first to sixth aspects of the invention.

A method for using blast furnace injection coal pertaining to an eighth aspect of the invention which solves the above problems comprises injecting blast furnace injection coal obtained by the method for preparing blast furnace injection coal pertaining to any one of the above-described first to sixth aspects of the invention through a tuyere into an interior of a blast furnace main body of a blast furnace installation.

Effect of the Invention

According to the present invention, the metal supported on the coal is in the form of nanoparticles and is uniformly dispersed in the coal, and the uniform mixing of the combustion ash, the metal in the form of the nanoparticles, and the slag in the blast furnace main body together is accelerated. Hence, it is possible to obtain blast furnace injection coal which is resistant to fluidity failure of slag in the blast furnace main body, even when the amount of the coal injected into the blast furnace main body is increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating a procedure of a method for preparing blast furnace injection coal pertaining to an embodiment of the present invention.

FIG. 2 is a quaternary phase diagram for SiO₂—CaO—MgO—20% Al₂O₃, where the total weight of Al, Si, Ca, and Mg oxides in the ash of coal used in the method for preparing blast furnace injection coal pertaining to an embodiment of the present invention is taken as 100% by weight, and the Al₂O₃ content is taken as 20% by weight.

FIG. 3 is a graph which illustrates the relationship between the (CaO+MgO)/SiO₂ weight ratio and the ash melting point and which is used in the method for preparing blast furnace injection coal pertaining to an embodiment of the present invention.

MODE FOR CARRYING OUT THE INVENTION

Embodiments of a method for preparing blast furnace injection, coal, blast furnace injection coal, and a method for using the blast furnace injection coal pertaining to the present invention will be described based on the drawings, but the present invention is not limited only to the following embodiments described based on the drawings.

An embodiment, of the method for preparing blast furnace injection coal, the blast furnace injection coal, and the method for using the blast furnace injection coal pertaining to the present invention will be described based on FIGS. 1 to 3.

The blast furnace injection coal pertaining to this embodiment is blast furnace injection coal to be injected through a tuyere into an interior of a blast furnace main body of a blast furnace installation, and, as shown in FIG. 1, can be easily prepared as follows. Specifically, ash of run-of-mine coal is analyzed, and the weight percentages of Al, Si, Ca, and Mg in the ash of the coal is analyzed (first step S1); an ash melting point of the coal is derived based on data obtained by the analysis (second step S2); a metal species to be supported on the coal is selected and the amount of the metal to be supported on the coal is derived based on the derived ash melting point of the coal (third step S3); the metal in the amount to be supported is supported based on data obtained in the third step S3 onto the coal by an ion exchange method (fourth step S4); and the coal supporting the metal (hereinafter, referred to as metal-supporting coal) is pyrolyzed (fifth step S5).

In the first step S1, the composition of the ash of run-of-mine coal is the data most basically used as the quality of coal (run-of-mine coal), and it is possible to use the data obtained by, for example, the industrial analysis set forth in JIS M 8812 (2004) implemented when the run-of-mine coal is produced or used.

In the first step S1, the weight percentages of Al, Si, Ca, and Ma in the ash of coal are the data most basically used as the quality of coal (run-of-mine coal), and it is possible to use the data obtained by, for example, the method for analyzing metals in exhaust gas (a method based on ICP (high-frequency inductively coupled plasma)) set forth in JIS K 0083, or the method for analyzing the coal ash and the coke ash set forth in JIS M 8815 implemented, when the run-of-mine coal is produced or used.

It is preferable to use, for example, a low-grade coal (oxygen atom content (dry base): higher than 18% by weight; average pore diameter: 3 to 4 nm) generally having many carboxy groups (—COOH) and hydroxy groups (—OH) such as lignite or sub-bituminous coal as the coal (run-of-mine coal) analyzed in the first step S1.

In the second step S2, the ash melting point of the coal can be derived, based on the data obtained in the first step S1 (the weight percentages of Al, Si, Ca, and Mg in the ash of the coal), by taking the Al, Si, Ca, and Mg oxides in the ash as 100% by weight, converting the Al₂O₃ content to 20% by weight, and using, for example, a quaternary phase diagram for SiO₂—CaO—MgO—20% Al₂O₃ shown in FIG. 2.

In the third step S3, the metal species to he supported on the coal is preferably selected based on the data obtained in the first step S1 (the weight percentages of SiO₂, CaO, and MgO, where the Al, Si, Ca, and Kg oxides in the ash is taken as 100% by weight, and the Al₂O₃ content is converted to 20% by weight) and the data obtained in the second step S2 (the ash melting point of the coal).

As the species of metal (metal species), it is preferable to select, for example, at least one of alkaline earth metals such as magnesium (Mg) and calcium (Ca). Especially when the silicon (Si) content in the ash of the coal is high (the weight percentage of SiO₂ is, for example, 75% by weight or higher), and the melting point of the ash is high (for example, 1500° C. or higher), it is preferable to support calcium (Ca) on the coal.

In the third step S3, the supported amount of the metal to be supported on the coal is preferably derived based on the data obtained in the first step (the weight percentages of SiO₂, CaO, and MgO, where the Al, Si, Ca, and Mg oxides in the ash is taken as 100% by weight, and the Al₂O₃ content is converted to 20% by weight, as well as the ash melting point of the coal), and the metal selected in the third step S3.

In the fourth step S4, the metal-supporting coal can be obtained by, for example, immersing the coal in an aqueous alkaline solution of the metal (for example, Ca(OH)₂, Mg(OH)₂, or the like) for a certain period (for example, 1 hour to 8 hours), followed by dehydration.

In the fifth step S5, the metal-supporting coal is preferably thermally treated in a thermal treatment furnace such as a kiln at, for example, 350 to 550° C. for, for example, 30 minutes to 2 hours to adjust a residual volatile content to 15 to 35%. This results in formation of nanoparticles (several ten nanometers to several hundred nanometers) of the metal, so that the metal is uniformly dispersed in the obtained blast furnace injection coal.

The blast furnace injection coal produced by the method for preparing blast furnace injection coal pertaining to this embodiment is obtained by supporting the metal on the coal by an ion exchange method and pyrolyzing the coal supporting the metal to adjust the ash melting point of the coal to lower than 1400° C. with the Al, Si, Ca, and Mg oxides in the ash of the coal being taken as 100% by weight, and the Al₂O₃ content in the ash being taken as 20% by weight. Hence, the metal supported on the coal is converted into nanoparticles, and uniformly dispersed in the coal. This accelerates the uniform mixing of the combustion ash, the metal in the form of the nanoparticles, and the slag in the blast furnace main body together. Therefore, it is possible to obtain blast furnace injection coal which is resistant to fluidity failure of the slag in the blast furnace main body, even when the amount of the coal injected into the blast furnace main body is increased. This makes it possible to reduce the amount of coke used.

Moreover, the metal in the form of the nanoparticles exerts a catalytic action, and can promote the combustion and gasification reactions in the presence of oxygen even at low temperature.

The ash of the coal and the metal are dispersed in the coal, and the mixing of the metal in the form of the nanoparticles, the combustion ash, and the slag is started after the coal is combusted. Hence, by converting the metal into the form of the nanoparticles before the coal is injected into the tuyere of the blast furnace main body, the combustion starts and ends earlier, and the mixing is started earlier, so that the speed of the uniform mixing increases.

Since the coal is pyrolyzed before being injected into the tuyere of the blast furnace main body, heat for thermal decomposition is unnecessary, and the amount of generated inactive thermal decomposition gas decreases. Hence, the combustion temperature increases, and the combustion speed increases, so that the combustion is completed earlier, and the mixing is started earlier.

In other words, by pyrolyzing the coal before being injected into the tuyere of the blast furnace main body, properties of the coal are changed and the metal is converted into nanoparticles. Consequently, the combustion is accelerated, so that the metal in the form of the nanoparticles, the combusted coal, and the slag are mixed together earlier, and the uniform mixing thereof is accelerated. This results in increase in fluidity of the mixture slag, and the dischargeability is improved.

Since the flux is injected in Patent Document 2 mentioned above, it is necessary to provide each blast furnace with a storage tank and an injection nozzle for the flux, so that the apparatus is complicated according to the number of the blast furnaces. However, since desired blast furnace injection coal can be obtained in this embodiment, the apparatus is not complicated, and the reliability of operations of the blast furnace can be increased.

Note that, when calcium is supported on the coal, the total weight percentage of calcium oxide (CaO) and magnesium oxide (MgO) relative to the weight percentage of silica (SiO₂) is preferably 0.2 (=0.14/0.66) or higher and 1.55 (=0.486/0.314) or lower, more preferably 0.25 (=0.16/0.64) or higher and 1.4 (=0.47/0.33) or lower, and further preferably 0.35 (=0.208/0.592) or higher and 1 (=0.4/0.4) or lower, where the total weight of Al, Si, Ca, and Mg oxides in the ash of the coal is taken as 100% by weight, and the Al₂O₃ content is converted to 20% by weight. In other words, calcium oxide is preferably supported on the coal with the total weight percentage of calcium oxide (CaO) and magnesium oxide (MgO) being 14% by weight to 48% by weight, calcium oxide is more preferably supported on the coal with the total weight percentage of calcium oxide (CaO) and magnesium oxide (MgO) being 16% by weight to 47% by weight, and calcium oxide is further preferably supported on the coal with the total weight percentage of calcium oxide (CaO) and magnesium oxide (MgO) being 21% by weight to 40% by weight. This is because various kinds of coal for which the composition of the ash and the ash melting point have been already known can be summarized as shown by black circles in FIG. 3, when attention is focused on the weight ratio of calcium oxide and magnesium oxide to silica and the ash melting point, and the approximate line of these data is as shown by the curve L1 in FIG. 3. In other words, as shown in FIG. 3, a (CaO+MgO)/SiO₂ ratio of lower than 0.2 or higher than 1.55 is not preferable, because the ash melting point of the blast furnace injection coal becomes higher than 1400° C., a (CaO+MgO)/SiO₂ ratio of lower than 0.25 or higher than 1.4 is not preferable, because the ash melting point of the blast-furnace injection coal becomes higher than 1300° C., and a (CaO+MgO)/SiO₂ ratio of lower than 0.35 or higher than 1 is not preferable, because the ash melting point of the blast furnace injection coal becomes higher than 1200° C.

Other Embodiments

Hereinabove, the method for preparing blast, furnace injection coal in which an alkaline earth metal such as Mg or Ca is supported on the coal by an ion exchange method; however, it is also possible to employ a method for preparing blast furnace injection coal in which an alkaline earth metal such as beryllium (Be) is supported as the metal on the coal. Such a method for preparing blast furnace injection coal also achieves the same operations and effect as those of the method for preparing blast furnace injection coal pertaining to the above-described embodiment.

It is also possible to employ a method for preparing blast furnace injection coal in which a boron-group element such as aluminum (Al) is supported on the coal. Such a method for preparing blast furnace injection coal also achieves the same operations and effect, as those of the method for preparing blast furnace injection coal pertaining to the above-described embodiment.

It is also possible to employ a method for preparing blast furnace injection coal in which an alkali metal such as Li, Na, or K is supported on the coal. Such a method for preparing blast furnace injection coal also achieves the same operations and effect as those of the method for preparing blast furnace injection coal pertaining to the above-described embodiment.

EXAMPLES

Working examples performed to confirm the operation and effect of the method for preparing blast furnace injection coal pertaining to the present invention will be described below, but the present invention is not limited to only the following working examples described based on various data.

First, as illustrated in FIG. 1, the moisture content of the coal of a coal type A in the run-of-mine coal state and the ash of the coal are analyzed, and the weight percentages of Al, Si, Ca, and Mg in the ash of the coal are analyzed in advance (first step S1).

TABLE 1 Coal Unit type A Compo- SiO₂ wt % 57.8 sition Al₂O₃ wt % 14.9 of ash TiO₂ wt % 0.84 Fe₂O₃ wt % 17.9 CaO wt % 1.71 MgO wt % 0.8 Na₂O wt % 0.39 K₂O wt % 2.25 SO₃ wt % 1.76 P₂O₃ wt % 0.1 Total of SiO₂, Al₂O₃, CaO, and MgO wt % 75.21 SiO₂ (converted with SiO₂, Al₂O₃, CaO, wt % 76.9 and MgO taken as 100 wt %) Al₂O₃ (converted with SiO₂, Al₂O₃, wt % 19.8 CaO, and MgO taken as 100 wt %) CaO (converted with SiO₂, Al₂O₃, CaO, wt % 2.3 and MgO taken as 100 wt %) MgO (converted with SiO₂, Al₂O₃, CaO, wt % 1.1 and MgO taken as 100 wt %) SiO₂ (converted with SiO₂, CaO, and wt % 76.6 MgO taken as 80 wt %) CaO (converted with SiO₂, CaO, and wt % 2.3 MgO taken as 80 wt %) MgO (converted with SiO₂, CaO, and wt % 1.1 MgO taken as 80 wt %)

In the coal type A described above, the contents of the oxides of Si, Ca, and Mg in the ash of the coal type A are values shown in Table 1 above, where the total weight of Al, Si, Ca, and Mg oxides in the ash of the coal type A is taken as 100% by weight, and the Al₂O₃ content, is converted to 20% by weight. Accordingly, the ash melting point of the coal type A is located at the coal type A in FIG. 2, which is a quaternary phase diagram for SiO₂—CaO—MgO—20% Al₂O₃, where the Al, Si, Ca, and Mg oxides in ash of coal is taken as 100% by weight, and the Al₂O₃ content is converted to 20% by weight.

Subsequently, the ash melting point of the coal type A is determined by using, for example, FIG. 2 based on the CaO content, the MgO content, and the SiO₂ content in the ash, where the total weight, of Al, Si, Ca, and Mg oxides in the ash of the coal type A is taken as 100% by weight, and the Al₂O₃ content is converted to 20% by weight.

Subsequently, a metal species to be supported on the coal type A is selected and the amount of the selected metal to be supported on the coal type A is derived based on the ash melting point of the coal type A and the region where the ash melting point of coal is lower than 1400. Here, it can be seen that the ash melting point of the coal can be 1400° C. or lower, when CaO at a ratio of approximately 10% by weight is supported on the coal type A. Hence, CaO is selected as the metal species to be supported on the coal type A, and 10% by weight is derived as the amount of the metal species to be supported.

Subsequently, the CaO is supported on the coal type A by an ion exchange method, followed by pyrolysis. Thus, blast furnace injection coal having an ash melting point, of 1400° C. or lower can be obtained.

Accordingly, these working examples reveal the following fact. Specifically, when the ash of run-of-mine coal is analyzed and the weight percentages of Al, Si, Ca, and Mg in the ash of the coal are analyzed, the ash melting point of the coal is derived based on data obtained by the analysis, CaO (metal species) to be supported on the coal is selected and the amount thereof to be supported is derived based on the obtained data to adjust the ash melting point of the coal to 1200 to 1400° C., and the metal in the amount to be supported is supported on the coal by an ion exchange method, followed by pyrolysis, the metal supported on the coal is converted to nanoparticles and uniformly dispersed in the coal, and the uniform mixing of the combustion ash, the metal in the form of the nanoparticles, and the slag in the blast furnace main body is accelerated, and, hence, it is possible to obtain blast furnace injection coal which is resistant to fluidity failure of slag in a blast furnace main body, even when the amount of the coal injected into the blast furnace main body is increased.

INDUSTRIAL APPLICABILITY

The present invention makes it possible to obtain blast furnace injection coal which is resistant to fluidity failure of slag in a blast furnace main body, even when the amount of the coal injected into the blast furnace main body is increased. Hence, the present invention can be extremely advantageously used in iron manufacturing industries.

EXPLANATION OF REFERENCE NUMERALS

L1 approximate line obtained from data (line showing relationship between (CaO+MgO)/SiO₂ and ash melting point of blast furnace injection coal) S1 first step (analysis step) S2 second step (step of deriving ash melting point of coal) S3 third step (step of selecting metal species to be supported and deriving amount thereof to be supported) S4 fourth step (supporting step) S5 fifth step (pyrolysis step) 

1. A method for preparing blast furnace injection coal to be injected through a tuyere into an interior of a blast furnace main body of a blast furnace installation, the method comprising: a first step of analyzing ash of run-of-mine coal and weight percentages of Al, Si, Ca, and Mg in the ash; a second step of deriving an ash melting point of the coal based on data obtained by the analysis; a third step of selecting a metal species to be supported on the coal and deriving the amount of the metal species to be supported based on data obtained in the first step and the second step to adjust the ash melting point of the coal to 1200 to 1400° C.; a fourth step of supporting the metal in the amount to be supported onto the coal by an ion exchange method; and a fifth step of pyrolyzing the coal obtained in the fourth step.
 2. The method for preparing blast furnace injection coal according to claim 1, wherein the metal is at least one of calcium and magnesium.
 3. The method for preparing blast furnace injection coal according to claim 1, wherein the coal is thermally treated at 350 to 550° C. in the fifth step to adjust a residual volatile content to 15 to 35%.
 4. The method for preparing blast furnace injection coal according to claim 1, wherein the amount of the metal to be supported on the coal is 0.2 to 1.55 in terms of (CaO+MgO)/SiO₂ weight ratio.
 5. The method for preparing blast furnace injection coal according to claim 4, wherein the amount of the metal to be supported on the coal is 0.25 to 1.4 in terms of (CaO+MgO)/SiO₂ weight ratio.
 6. The method for preparing blast furnace injection coal according to claim 5, wherein the amount of the metal to be supported on the coal is 0.35 to 1 in terms of (CaO+MgO)/SiO₂ weight ratio.
 7. Blast furnace injection coal, which is obtained by the method for preparing blast furnace injection coal according to claim
 1. 8. A method for using blast furnace injection coal, the method comprising injecting blast furnace injection coal obtained by the method for preparing blast furnace injection coal according to claim 1 through a tuyere into an interior of a blast furnace main body of a blast furnace installation. 